In typical video compression systems and standards, such as MPEG-2 and JVT/H.264/MPEG AVC, encoders and decoders generally rely on intra and inter coding in order to achieve compression. In intra coding, spatial prediction methods are used; while for inter coding, compression is achieved by exploiting the temporal correlation that may exist between pictures. More specifically, previously encoded/decoded pictures are used as references for future pictures, while motion estimation and compensation are employed in order to compensate for any motion activity between these pictures. More advanced CODECs such as H.264 also consider lighting variations, such as during a fade in/out, in order to generate a more accurate prediction, when necessary. Finally, deblocking methods may also be used in an effort to reduce blocking artifacts created through the prediction and quantization processes.
Unfortunately, the typical methods related to inter coding fail to consider some additional properties and features that may considerably affect the entire prediction process. In particular, especially at higher resolutions, a picture may contain several types of noise, such as film grain or speckle noise. This kind of noise tends to be completely uncorrelated from one picture to the other, which would imply that any remaining noise within a reference picture would most likely need to be compensated during the encoding process. Although some of this noise may be removed through the quantization process and possibly through non-normative thresholding introduced in the encoder, it can still have a considerable negative impact in coding efficiency.
It is possible to remove this noise in a pre-processing stage, where temporal and spatial filtering methods can be used, thus allowing a considerable improvement in encoding efficiency; but it might also be desirable to retain, such as in the case of film content, some of this noise since it may itself be part of the artistic content of the film. Accordingly, what is needed is a new scheme to reduce uncorrelated noise in reference pictures while maintaining the artistic content of the displayed pictures.